This document provides an introduction to the Semantic Web and the technologies that enable it. It defines key concepts like resources, URIs, RDF, RDF Schema (RDFS), and the Web Ontology Language (OWL). It explains how these technologies allow data on the web to be represented and linked in a standardized, machine-readable way. Examples are provided to illustrate how RDF and OWL can be used to represent relationships between resources like books and authors. The document discusses how semantic technologies can help integrate and combine data from diverse sources on the web.

1. https://elite.polito.it
SEMANTIC WEB
AN INTRODUCTION
Luigi De Russis
@luigidr

2. THE WEB IS A WEB OF DOCUMENT FOR PEOPLE,
NOT FOR MACHINES 2

3. THE WEB IS A WEB OF DOCUMENT
3

4. THE SEMANTIC WEB IS A WEB OF DATA
Linking Open Data cloud diagram,
by Richard Cyganiak and Anja Jentzsch.
http://lod-cloud.net/ 4

5. THINK

6. HOW TO GET DATA FROM THE WEB?
AN EXAMPLE
We would like to create an online catalog of all the
Computer Engineering degrees at university level
6

7. HOW TO GET DATA FROM THE WEB?
AN EXAMPLE
We would like to create an online catalog of all the
Computer Engineering degrees at university level
7

8. HOW TO GET DATA FROM THE WEB?
Data is locked in
"data islands"
Limited or no
access to this
data
8

9. DATA SHOULD BE AVAILABLE ON THE WEB
ACCESSIBLE AND STRUCTURED VIA STANDARD WEB TECHNOLOGIES
NOT CONTROLLED BY APPLICATIONS, ONLY
DATA SHOULD BE INTERLINKED OVER THE WEB
I.E., DATA CAN BE INTEGRATED OVER THE WEB
THIS IS WHERE THE SEMANTIC WEB COMES IN
DATA ON THE WEB IS NOT ENOUGH
WE NEED A PROPER INFRASTRUCTURE
9

10. DEFINITIONS

11. To a computer, the Web is a flat, boring world,
devoid of meaning. This is a pity, as in fact
documents on the Web describe real objects and
imaginary concepts. […]
Adding semantics to the Web involves two things:
allowing documents which have information in
machine-readable forms, and allowing links to be
created with relationship values. Only when we have
this extra level of semantics we will be able to use
computer power to help us exploit the information
to a greater extent than our own reading.
TIM BERNERS-LEE, 1994
11

12. THE WEB, 1994 C.A.
NEW!
NEW!
NO GOOGLE, WIKIPEDIA, AMAZON,
… YET!
12

13. I have a dream for the Web [in which computers]
become capable of analyzing all the data on the
Web – the content, links, and transaction between
people and computers.
A “Semantic Web”, which should make this possible,
has yet to emerge, but when it does, the day-to-day
mechanisms of trade, bureaucracy and our daily
lives will be handled by machines talking to
machines. The “intelligent agents” people have
touted for ages will finally materialize.
TIM BERNERS-LEE, 1999
Weaving the Web – The Original Design and Ultimate Destiny of the World Wide Web by Its Inventor.
Tim Berners-Lee, Harper San Francisco, September 1999 13

14. THE SEMANTIC WEB IS THE WEB
SAME BASE TECHNOLOGIES, EVOLUTIONARY, DECENTRALIZED
IT IS ABOUT COMMON FORMATS
FOR INTEGRATION AND COMBINATION OF DATA DRAWN FROM
DIVERSE SOURCES
IT IS ABOUT A LANGUAGE
FOR RECORDING HOW THE DATA RELATES TO REAL WORLD OBJECTS
THE SEMANTIC WEB IS A WEB OF DATA
14

15. FUNDAMENTALS

16. RESOURCE
EVERY DOCUMENT "REACHABLE" ON THE WEB
NO MATTER THE CONTENT, FORMAT, LANGUAGE, ETC.
RESOURCE AND DESCRIPTION
RESOURCE DESCRIPTION
INDEPENDENT FROM THE FORMAT
STANDARD LANGUAGE (BASED ON METADATA)
16

17. RESOURCES
17

18. DESCRIPTION
18

19. Title
Author
Date
Topic
Quality
Title
Author
Date
Topic
19
DESCRIPTION

20. 20

21. URIs
SPARQL
RDFS, OWL
RDF
OWL, SWRL
21

22. URIs
SPARQL
RDFS, OWL
RDF
Unambiguous names
for resources
OWL, SWRL
22

23. URIs
SPARQL
RDFS, OWL
RDF
A common data
model to connect
and describe
resources
OWL, SWRL
23

24. URIs
SPARQL
RDFS, OWL
RDF
Access to
the data
model
OWL, SWRL
24

25. URIs
SPARQL
RDFS, OWL
RDF
Common description
languages
OWL, SWRL
25

26. URIs
SPARQL
RDFS, OWL
OWL, SWRL
RDF
Reasoning, mainly logic inference,
and rules
26

27. URIs
SPARQL
RDFS, OWL
RDF
OWL, SWRL
OK, IT'S TIME TO COOK!

28. MODELING DATA

29. REPRESENT THE FOLLOWING DATA ABOUT THE AI BOOK
AS A SET OF RELATIONS
TITLE: “ARTIFICIAL INTELLIGENCE: A MODERN APPROACH”
AUTHOR: RUSSEL, STUART AND NORVIG, PETER
PUBLISHER: PRENTICE HALL
ISBN: 978-0136042594
EXAMPLE: BOOKSTORE
29

30. http://...isbn/978013604
2594
Resource
30
EXAMPLE: BOOKSTORE

31. http://...isbn/978013604
2594
Artificial Intelligence: A
Modern Approach
Literal
31
EXAMPLE: BOOKSTORE

32. http://...isbn/978013604
2594
Artificial Intelligence: A
Modern Approach
title
32
EXAMPLE: BOOKSTORE

33. http://...isbn/978013604
2594
Artificial Intelligence: A
Modern Approach
Prentice Hall
Russel, Stuart
Norvig, Peter
title
publisher
author
author
33
EXAMPLE: BOOKSTORE

34. RDF: RESOURCE DESCRIPTION FRAMEWORK
STRUCTURED IN STATEMENTS
SUBJECT
A RESOURCE (URI)
PREDICATE
A VERB, PROPERTY, OR RELATIONSHIP
OBJECT
A RESOURCE OR A LITERAL STRING
http://...isbn/978013604
2594
author
Norvig, Peter
34

35. http://...isbn/978013604
2594
Artificial Intelligence: A
Modern Approach
Prentice Hall
Russel, Stuart
Norvig, Peter
title
publisher
author
author
Subject
Predicate
Predicate
Predicates
Object
Object
Object
Object
35
EXAMPLE: BOOKSTORE

36. http://...isbn/978013604
2594
Artificial Intelligence: A
Modern Approach
title
RDF IN XML SYNTAX
<rdf:RDF xmlns:rdf=http://www.w3.org/…/22-rdf-syntax-ns#>
<rdf:Description about="http://... isbn/9780136042594">
<title>Artificial Intelligence: A Modern Approach</title>
</rdf:Description>
</RDF>
36
EXAMPLE: BOOKSTORE

37. http://...isbn/978013604
2594
Artificial Intelligence: A
Modern Approach
title
RDF IN TURLE
<http://... isbn/9780136042594>
title "Artificial Intelligence: A Modern Approach"
37
EXAMPLE: BOOKSTORE

38. LINKING DATA

39. REPRESENT THE FOLLOWING DATA ABOUT THE ITALIAN
TRANSLATION OF THE AI BOOK AS A SET OF RELATIONS
TITLE: “INTELLIGENZA ARTIFICIALE. UN APPROCCIO
MODERNO”
AUTHOR: RUSSEL, STUART AND NORVIG, PETER
PUBLISHER: PRENTICE HALL
ISBN: 978-8871925936
ORIGINAL ISBN: 978-0136042594
EXAMPLE: BOOKSTORE
39

40. http://...isbn/978013604
2594
Intelligenza Artificiale. Un
approccio moderno
Prentice Hall
Russel, Stuart
Norvig, Peter
title
publisher
creator
creator
EXAMPLE: BOOKSTORE
http://...isbn/978887192
5936
original
40

41. http://...isbn/978013604
2594
Intelligenza Artificiale. Un
approccio moderno
Prentice Hall
title
publisher
EXAMPLE: BOOKSTORE
http://...isbn/978887192
5936
original
http://...isbn/978013604
2594
Artificial Intelligence: A
Modern Approach
Prentice Hall
title
publisher
41

42. same URI, same resource
http://...isbn/978013604
2594
Intelligenza Artificiale. Un
approccio moderno
Prentice Hall
title
publisher
EXAMPLE: BOOKSTORE
http://...isbn/978887192
5936
original
http://...isbn/978013604
2594
Artificial Intelligence: A
Modern Approach
Prentice Hall
title
publisher
42

43. http://...isbn/978013604
2594
Intelligenza Artificiale. Un
approccio moderno
Prentice Hall
title
publisher
EXAMPLE: BOOKSTORE
http://...isbn/978887192
5936
original
Artificial Intelligence: A
Modern Approach
Prentice Hall
title
publisher
Russel, Stuart
Norvig, Peter
creator
creator
Russel, Stuart
author
author
Norvig, Peter
43

44. http://...isbn/978013604
2594
Intelligenza Artificiale. Un
approccio moderno
Prentice Hall
title
publisher
EXAMPLE: BOOKSTORE
http://...isbn/978887192
5936
original
Artificial Intelligence: A
Modern Approach
Prentice Hall
title
publisher
Russel, Stuart
Norvig, Peter
creator
creator
Russel, Stuart
author
author
Norvig, Peter
WHAT ABOUT MERGING CREATOR AND
AUTHOR?
IN RDF IT IS NOT POSSIBLE

45. SYNONYMS
AUTHOR OR CREATOR OR MAKER OR
CONTRIBUTOR OR…
SINGULAR OR PLURAL
AUTHOR OR AUTHORS
SOLUTION: STANDARDS
GENERAL OR DOMAIN-SPECIFIC
PROBLEM: FIELD NAMES ARE ARBITRARY
PROBLEM: FIELD VALUES ARE ARBITRARY
VALUE TYPE
STRING, DATE, INTEGER…
VALUE FORMAT
"NORVIG, PETER" OR " NORVIG, P." OR
"PETER NORVIG" OR…
VALUE RESTRICTIONS
ONE VALUE OR MULTIPLE VALUES (HOW
MANY?)
SOLUTIONS:
STANDARDS
CONTROLLED VOCABULARY
SEMANTICALLY RICH
DESCRIPTIONS
45

46. DUBLIN CORE
GENERAL VOCABULARY
DUBLIN CORE METADATA INITIATIVE (DCMI)
HTTP://DUBLINCORE.ORG
BUILDING BLOCKS TO DEFINE METADATA FOR THE
SEMANTIC WEB
DEFINE TITLE, CONTRIBUTOR, PUBLISHER, LICENSE, DATE, LANGUAGE, ETC.
46

47. FRIEND OF A FRIEND (FOAF)
GENERAL ONTOLOGY
DESCRIBE PERSONS, THEIR ACTIVITIES AND THEIR RELATIONS TO OTHER
PEOPLE AND OBJECTS
HTTP://WWW.FOAF-PROJECT.ORG
BUILDING BLOCKS TO DEFINE STRUCTURED
RELATIONS BETWEEN PEOPLE
DEFINE NAME, FAMILYNAME, GIVENNAME, KNOWS, AGE, NICK, ETC.
47

48. EXAMPLE: BOOKSTORE
http://...isbn/978013604
2594
Artificial Intelligence: A
Modern Approach
Prentice Hall
Russel, Stuart
Norvig, Peter
dc:title
dc:publisherdc:creator
foaf:name
foaf:name
dc:creator
foaf:name
foaf: http://xmlns.com/foaf/spec
dc: http://purl.org/dc/terms
48

49. WHY?
http://...isbn/978013604
2594
Norvig, Peter
dc:creator
foaf:name
http://...isbn/978013604
2594
Norvig, Peter
author
49

50. RDF SCHEMA

51. RDF SCHEMA (RDFS)
SCHEMA
DEFINITION OF THE NODES AND PREDICATES USED IN A RDF DOCUMENT
RDFS CAN BE SEE AS A "META-MODEL"
DOMAIN AND RANGE
RDFS DESCRIBES PROPERTIES IN TERMS OF CLASSES OF RESOURCE
TO WHICH THEY APPLY
(FROM A "DOMAIN" TO A "RANGE")
51

52. EXAMPLE
http://elite.polito.it/people/
derussis teaches
http://bit.ly/polito-
ami
RDF data
52

53. RDF data
http://elite.polito.it/people/
derussis teaches
http://bit.ly/polito-
ami
Teacher
Person
teaches Course
domain range
subClassOf
type
type
RDF schema
53
EXAMPLE

54. BACK TO THE BOOKSTORE EXAMPLE…
http://...isbn/978013604
2594
Norvig, Peter
dc:creator
foaf:name
http://...isbn/978013604
2594
Norvig, Peter
author WHY?
54

55. BACK TO THE BOOKSTORE EXAMPLE…
http://...isbn/978013604
2594
Norvig, Peter
dc:creator
foaf:name
http://...isbn/978013604
2594
Norvig, Peter
author WHY?
DC:CREATOR HAS RANGE AGENT, I.E., A CLASS (RESOURCE), NOT A LITERAL:
WE USE AN ANONYMOUS CLASS FOR THIS SCOPE.
FINALLY, FOAF:NAME HAS RANGE RDFS:LITERAL.
55

56. RDFS EXPRESSIVITY
SIMPLE RELATIONSHIP BETWEEN THINGS
RDFS PROVIDES A VOCABULARY TO EXPRESS RELATIONSHIP BETWEEN
THINGS (E.G., SUBCLASSOF OR TYPE)
CANNOT DESCRIBE COMPLEX RELATIONSHIP
RDFS CANNOT DESCRIBE DATA IN TERMS OF SET OF OPERATIONS (E.G., UNIONOF),
EQUIVALENCE (E.G., SAMEAS)
OR CARDINALITY (E.G. ALLVALUEFROM)
56

57. OWL

58. WEB ONTOLOGY LANGUAGE (OWL)
KNOWLEDGE REPRESENTATION LANGUAGE
DESIGNED TO FORMULATE, EXCHANGE AND REASON WITH KNOWLEDGE
ABOUT A DOMAIN OF INTEREST
CURRENTLY, AT VERSION 2
ONTOLOGY
IT IS THE RESULT OF THE MODELING PROCESS
AN ONTOLOGY IS AN EXPLICIT DESCRIPTION OF A DOMAIN
IN TERMS OF CONCEPTS, PROPERTIES AND ATTRIBUTES OF CONCEPTS,
CONSTRAINTS ON PROPERTIES AND ATTRIBUTES, AND INDIVIDUALS
AN ONTOLOGY DEFINES A COMMON VOCABULARY
AND A SHARED UNDERSTANDING
58

59. INDIVIDUALS, CLASSES, AND PROPERTIES
EXAMPLES
"POLITECNICO DI TORINO IS A UNIVERSITY"
"POLITECNICO DI TORINO HAS A PROFESSOR NAMED ELIO PICCOLO"
"POLITECNICO DI TORINO" IS AN OBJECT: AN INDIVIDUAL IN OWL2
"UNIVERSITY" IS A CATEGORY: A CLASS IN OWL2
"HAS A PROFESSOR" IS A RELATION: A PROPERTY IN OWL2
"ELIO PICCOLO" IS AN INDIVIDUAL, TOO
59

60. OBJECT VS. DATA PROPERTIES
OBJECT PROPERTIES
RELATE OBJECTS TO OBJECTS
"POLITECNICO DI TORINO HAS A PROFESSOR NAMED ELIO PICCOLO"
DATA PROPERTIES
ASSIGN DATA VALUES TO OBJECTS
"THE PROFESSOR IS NAMED ELIO PICCOLO"
60

61. WEB ONTOLOGY LANGUAGE
EXPRESSIVITY
DESIGNED TO REPRESENT RICH AND COMPLEX KNOWLEDGE
ABOUT THINGS, GROUP OF THINGS, AND THEIR RELATIONSHIPS
LOGIC-BASED
KNOWLEDGE EXPRESSED IN OWL CAN BE REASONED WITH A COMPUTER PROGRAM
TO VERIFY ITS CONSISTENCY OR TO MAKE IMPLICIT KNOWLEDGE EXPLICIT
LINKED
ONTOLOGIES IN OWL CAN BE PUBLISHED ON THE WEB AND MY
REFER TO OR BE REFERRED FROM OTHER OWL ONTOLOGIES
CHOOSE THE SYNTAX YOU LIKE
VARIOUS SYNTAXES ARE AVAILABLE FOR OWL, FOR DIFFERENT PURPOSES
(RDF/XML, TURTLE, MANCHESTER, ETC.)
61

62. EXAMPLE: BOOKSTORE
Intelligenza Artificiale. Un
approccio moderno
Prentice Hall
dc:title
dc:publisher
Artificial Intelligence: A
Modern Approach
Prentice Hall
dc:title
dc:publisher
Libro
Book
rdfs:type
rdf:type
http://...isbn/97888719259
36
http://...isbn/9780136042
594
62

63. Intelligenza Artificiale. Un
approccio moderno
Prentice Hall
dc:title
dc:publisher
Artificial Intelligence: A
Modern Approach
Prentice Hall
dc:title
Libro
Book
rdfs:type
rdf:type
http://...isbn/97888719259
36
http://...isbn/9780136042
594
owl:sameAs
63
dc:publisher
EXAMPLE: BOOKSTORE

64. HANDS ON OWL2

65. TOOLS FOR OWL
EDITORS
MOST COMMON EDITOR: PROTÉGÉ 5
OTHER TOOLS: TOPBRAID COMPOSER, NEON TOOLKIT
SPECIAL PURPOSES APPS, ESP. FOR LIGHT-WEIGHT ONTOLOGIES
(E.G., FOAF EDITORS)
(http://semanticweb.org/wiki/Editors)
65
REASONERS
OWL DL: PELLET 2.0, HERMIT, FACT++, RACERPRO
OWL EL: CEL, SHER, SNOROCKET, ELLY
OWL RL: OWLIM, JENA, ORACLE OWL REASONER
OWL QL: OWLGRES, QUONTO, QUILL
(http://semanticweb.org/wiki/Reasoners)

66. ONTOLOGY ENGINEERING
A.K.A. THE PROCESS OF BUILDING AND MAINTAINING AN ONTOLOGY
WHY DEVELOP AN ONTOLOGY?
1. TO SHARE COMMON UNDERSTANDING OF THE STRUCTURE OF INFORMATION,
AMONG PEOPLE AND SOFTWARE ARTIFACTS
2. TO ENABLE REUSE OF DOMAIN KNOWLEDGE (STANDARDS)
3. TO MAKE DOMAIN ASSUMPTIONS EXPLICIT
4. TO SEPARATE DOMAIN KNOWLEDGE FROM THE OPERATIONAL KNOWLEDGE
HOW?
Determine
the scope
Consider
reuse
Enumerate
terms
Define
classes
Define
properties
Define
constraints
Create
instances
66

67. AN ONTOLOGY THAT DESCRIBES THE UNIVERSITY
DOMAIN FROM THE EDUCATIONAL PERSPECTIVE
(HOW MANY STUDENTS FOLLOW A COURSE, WHICH
DEGREES A UNIVERSITY OFFERS, WHO TEACHES A
SPECIFIC COURSE, ETC.)
EXAMPLE: THE UNIVERSITY ONTOLOGY
67

68. https://elite.polito.it
THANKS!
QUESTIONS?
Luigi De Russis
@luigidr
luigi.derussis@polito.it

69. REFERENCES
Semantic Web standards: http://w3c.org/standards/semanticweb
Semantic Web Wiki: http://semanticweb.org
Semantic Web FAQ: http://www.w3c.org/2001/sw/SW-FAQ
Book: A Semantic Web Primer (http://www.semanticwebprimer.org)
Book: Semantic Web Programming (http://semwebprogramming.org)
Semantic Web course @PoliTo: https://elite.polito.it/teaching/current-
courses/360-01rrdiu-semantic-web
69

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70